MIMO is an abbreviation of Multi-Input Multi-Output, and refers to a method of improving efficiency of data transmission and reception by adopting multiple transmit antennas and multiple receive antennas instead of using one transmit antenna and one receive antenna. That is, MIMI is a technology for enhancing capacity or improving performance using multiple antennas at the transmission end or reception end of a wireless communication system. Here, MIMO is also called multiple antennas.
In summary, multiple antenna technology applies collection of data fragments received from several antennas and completion of a message in order to receive one whole message without relying on a single antenna path. This is a next generation mobile communication technology which can be broadly applied to a mobile communication terminal and a relay, etc. because data transmission speed may be improved in a certain range and a system range may be increased with respect to specific data transmission speed. As such, this technology has drawn attention of those skilled in the art as a next generation technology capable of overcoming limitations of the amount of the transmission data of a mobile communication which has reached a limited situation due to extension of data communication.
Generally, when a transmission channel is in a deep fading state, if another version or replica of a transmission signal is not additionally transmitted, it is very difficult for a receiver to determine a transmitted signal. The source corresponding to the above mentioned other version or replica is called diversity, and this is a very important factor which contributes to performance of reliable transmission with respect to the wireless channel.
The use of diversity may maximize transfer capacity or transfer reliability. A system, which performs diversity using multiple transmit antennas and multiple receiving antennas, is also called a MIMO system or a multiple antenna system.
Likewise, in order to overcome performance deterioration by channel padding, a spatial diversity scheme using a MIMO system has been studied a lot.
A MIMO system provides advantages such as high data transfer rate, low error rate, and channel capacity enhancement, etc. by implementing two or more antennas to a transmitter and a receiver.
However, despite advantages of the MIMO system, it is generally impossible to implement a MIMO system in uplink due to restrictions on size, weight, hardware complexity, etc.
As an alternative, a cooperative diversity scheme has been suggested. The cooperative diversity scheme has advantages such as spatial diversity gain of a MIMO system, error rate reduction, channel capacity enhancement, etc. even when each terminal has only at least one antenna in a wireless communication network. To this end, the cooperative diversity scheme makes it possible to have advantages of a MIMO system using only one or more antennas by forming a virtual MIMO system as neighboring terminals share resources such as a frequency band with the antenna of a relay with a relay and a femtocell.
Likewise, the cooperative diversity scheme is based on use of a separate relay.
However, there is a need for cooperative transmission using terminals without a separate relay.